I loved my power pack, installation doesn't get easier and the power is noticeable. I would say if you want more bass you should get a mono amp and a sub set up, but the power pack will get you really good mids and highs.

I have an Alpine ida-x303 with Alpine SPS-600 speakers. It initially wasn't loud enough for me. When I open the windows the wind noise would drown out the system. I added the power pack for $109 from Best buy they installed it for free. The system is now perfect with plenty enough volume for me now, the sound has improved and is cleaner.
If you don't need a full on amp, the power pack will have plenty of juice. If you are into boom boom bass then get a true amp.

It adds about 40 watts to your system per Ch.. For the price and ease of install it can't be beat. As you said above get rid of those 4x6 over sized Pioneer tweeters and get a Kicker 4in mid with a 4x6 plate and enjoy the sound...